Variant responsive values not working alongside other responsive values

[julianbenegas]

Describe the bug
You have a component with the variant property inside sx. This variant holds a responsive value, say fontSize: ["12px", "16px"]. If you then put another responsive value to the sx, then the variant's responsive value won't work.

To Reproduce
Steps to reproduce the behavior:

1. Go to this sandbox
2. Resize the window
3. See that the text doesn't change size

Expected behaviour
The text should change it's fontSize

Additional context
It happens when using variant variant inside sx. If variant is used as a prop, it works as expected.

[jxnblk]

Thanks! This looks like an odd bug... possibly related to #720 and #832